(Newser)
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A student who was stabbed in the liver remains in critical condition following today's rampage at a high school in suburban Pittsburgh that left 23 others injured and a sophomore in custody. The suspect is 16-year-old Alex Hribal, and he has been charged as an adult with four counts of attempted homicide and 21 counts of aggravated assault. The motive remains unclear, but the AP says police are investigating reports of a threatening phone call between Hribal and another student last night. It wasn't clear which of the two made the call. The accounts of exactly what happened at Franklin Regional High School in Murrysville are still unfolding, but authorities say assistant principal Sam King and a security guard at the school tackled and subdued the attacker in a hallway. Some other details emerging:

The attack began in a classroom when Hribal pulled out two 8-inch kitchen knives and began slashing students, reports the Pittsburgh Post-Gazette. He reportedly followed them as they fled into the hallway and stabbed others as he ran.

During the assault, the attacker "was very quiet," student Mia Meixner tells CNN. "He just was kind of doing it. And he had this, like, look on his face that he was just crazy and he was just running around just stabbing whoever was in his way."

A doctor at a nearby hospital said a female student with "an amazing amount of composure" likely saved the life of one of the more seriously injured male students by applying pressure to his wounds.

That appears to be junior Gracie Evans, who recounts to the Pittsburgh newspaper: "My friend was on his stomach, and the other kid who was severely injured was told to sit up. I knew that wasn't right. I said to a few students, we need pressure on this wound, and they gave me some paper towels, and I held pressure on that wound for about 10 minutes."

Authorities say 22 people were stabbed or slashed, all but one of them students, and two more students suffered other injuries in the chaos.